Natural oakmoss is of importance to the fragrance industry. It is used in high grade perfume compositions such as lavender, chypre, and fougere. Unfortunately, the supply of natural oakmoss is limited. As a result, synthetic substitutes have been sought. Specifically, methyl 3,6-dimethyl-resorcylate and methyl 3-ethyl-6-methyl-resorcylate are important synthetics having oakmoss-like odors.
Several synthetic methods are known for preparing dialkyl resorcylic acid esters from the corresponding dihydroresorcylic acid esters. The dihydroresorcylic esters may be obtained by condensing malonic acid esters with .alpha., .beta.-unsaturated ketones. [U. Steiner and B. Willhalm, Helv. Chim. Acta, 35, 1752 (1952)]. The dihydroresorcylic acid esters may be aromatized by known methods. For example, a method reported by A. Sonn [Ber. Deut. Chem. Ges. 62B, 3012 (1929)] uses a palladium catalyst for aromatization. Another method employing chlorine gas is disclosed in Grossman, J. D. et al., U.S. Pat. No. 3,634,491 (1972). Aromatization via a bromination, dehalogenation sequence has also been reported. [Kulka, K. et al., U.S. Pat. No. 3,884,843 (1975), assigned to Fritzsche Dodge & Olcott Inc., New York, N.Y., the assignee herein.] Finally, Klein, E. et al., U.S. Pat. No. 4,142,053 (1979) discloses the aromatization of dihydro-.beta.-resorcylic acid esters with sulfuric acid and acetic anhydride, followed by saponification of the resulting diacetates.
Thus, there are a number of known methods for preparing resorcylic acid esters. However, there is no teaching or suggestion in the prior art of converting dihydroresorcylic acid esters to 3,6-dialkyl resorcylic acid esters according to the low cost, efficient process provided by this invention.